1. Field of the Invention
This invention relates to the read control of memories, and more particularly to a method of controlling a rotary memory such as a magnetic drum storage or magnetic disk storage.
2. Description of the Prior Art
A recording format as shown in FIG. 1 has heretofore been employed in a rotary memory, for example, a magnetic disk storage. Referring to FIG. 1, each individual track includes a plurality of information blocks R, and each of these blocks R comprises an address marker AM, a count area C, a key area K and a data area D arranged in the described order with a gap G interposed therebetween. The address marker AM represents the starting point of the block R, and the key area K represents the kind of data recorded in the data area D.
In the prior art format shown in FIG. 1, the presence of in information block R is detected when an address marker AM provided in the starting point of this block R is detected. When such an address marker AM is not detected within a predetermined searching range, this indicates either of the following two cases. In one case, no address marker AM is detected because no information block R that should follow an address marker AM is present; while in the other case, such address marker AM is not detected due to a failure of a control unit to properly detect the address marker AM during reading.
According to a prior art flow chart as shown in FIG. 4, the address marker searching operation proceeds, under control of a control unit, to the next one, thence to the end of a specific track, when no address marker AM is detected within a predetermined searching range. When no address marker AM is detected in spite of the searching operation which is continued to the end of the specific track, the control unit decides that the preceding information block R is the final one of the specific track and is not followed by any additional blocks R, and the reading operation is normal. When, on the other hand, an address marker AM is detected in the course of the searching operation which is continued to the end of the specific track, the control unit decides that the reading operation has merely failed to detect the address marker AM. This failure to detect an address marker AM is called a missing AM operation hereinafter. Upon decision that there has occured missing AM operation, the memory is controlled so that the missing record can be read. However, according to the prior art method of determining a missing AM operation, the address marker searching operation which is continued to the end of a specific track would not detect any address marker AM in the case in which the missed information block R is the final one of the specific track. Therefore, the prior art control method has been defective in that the control unit decides that the reading operation is normal in such a case, and that the failure to detect the AM marker results from the fact that there is no information block present.